The 510-joule rating means your computer, printer, scanner, external hard drive & other sensitive electronic components are protected against strong surges & spikes. This power surge protector with USB ports features full normal mode (H-N) & common mode (N-G / H-G) line surge suppression. It filters out disruptive EMI / RFI line noise that can cause equipment damage or data loss & exceeds IEEE 587 Category A & B surge suppression specifications. Features two USB ports that produce 3.1A of combined power to charge your mobile devices, including smartphones, tablets & MP3 players. A top storage shelf holds smartphones & other small devices while theyre charging. Three-plug surge protector mounts to a clamp that attaches to most desks, tables & flat surfaces, bringing power & device charging to your desktop. The ten-foot power cord has a NEMA 5-15P plug & fits through the back of the clamp to reduce cable clutter. Tripp Lite will repair or replace any connected equipment damaged by surges, including direct lightning strikes, up to $20,000 for life (valid in the U.S., Canada & Puerto Rico only.) Number of Outlets: 3 AC; 2 USB; Joules Of Surge Protection: 510 J; Lines: 3; Jacks: USB.